1. Field of the Invention
The present invention relates generally to an antenna for use on a missile or the like. More specifically, the present invention relates to a microstrip antenna which includes a GPS antenna for receiving GPS data and a telemetry antenna for transmitting telemetry data and which is adapted for use on small diameter devices such as a missile.
2. Description of the Prior Art
In the past military aircraft and weapons systems such as airplanes, target drones, pods and missiles have included flight termination and beacon tracking antenna to monitor performance during test flights. For example, a missile under test will always have an antenna which is generally surface mounted to transmit telemetry data to a ground station. The ground station then performs an analysis of the telemetry data from the missile to determine its performance during flight while tracking a target.
U.S. Pat. No. 4,356,492 is an example of a prior art microstrip antenna which is adapted for use on a missile as a wrap around band to a missile body without interfering with the aerodynamic design of the missile. U.S. Pat. No. 4,356,492 teaches a plurality of separate radiating elements which operate at widely separated frequencies from a single common input point. The common input point is fed at all the desired frequencies from a single transmission feed line.
With the emerging use of the Global Positioning System (GPS) for tracking purposes, there is a need to include GPS within the instrumentation package for a missile and target drone to accurately measure flight performance. GPS data is extremely accurate and thus allows for a thorough analysis of the missile""s performance as well as the target drone""s performance in flight while the missile tracks the target drone on a course to intercept the target drone.
The use of satellite provided GPS data to monitor the position of a missile and a drone target in flight will require that an antenna for receiving the GPS data be included in the instrumentation package. The receiving antenna should preferably be mounted on the same dielectric substrate as the transmitting antenna so that the antenna assembly can be applied readily as a wrap around band to the missile body without interfering with the aerodynamic design of the missile. Similarly, the antenna assembly which would include a GPS data receiving antenna and telemetry data transmitting antenna configured as a wrap around band to the projectile""s body without interfering with the aerodynamic design of the projectile.
The present invention overcomes some of the disadvantages of the past including those mentioned above in that it comprises a relatively simple in design yet highly effective and efficient microstrip antenna assembly which can receive satellite provided GPS position and also transmit telemetry data. The microstrip antenna comprising the present invention is configured to wrap around the projectile""s body without interfering with the aerodynamic design of the projectile.
The antenna assembly of the present invention includes a first microstrip antenna which is a telemetry antenna mounted on a dielectric substrate. The telemetry antenna transmits telemetry data to ground station or other receiving station. There is also a second microstrip antenna mounted on the dielectric substrate which is physically separated from the first microstrip antenna on the dielectric substrate. The second microstrip antenna is a GPS antenna adapted to receive satellite provided GPS position data. The antenna assembly is a wrap around antenna assembly which fits on the outer surface of a missile, target drone or any other small diameter projectile.
The telemetry antenna includes a pair of radiating elements with one radiating element being positioned on one side of the projectile and the other element being positioned on the opposite side of the projectile. One of the two radiating elements of the telemetry antenna has a feed line which provides for a 180 degree phase shift of the transmitted RF signal relative to the feed line for the other radiating element. This phase shift insures that the electric field for the transmitted RF signal is continuous around the circumference of the projectile.
The GPS antenna also has a pair of microstrip receiving antenna elements which are circularly polarized. Due to the close proximity of the telemetry and GPS antennas each antenna includes a band stop filter which are integrated into the GPS and telemetry antennas. The band stop filters have a minimum stop-band rejection of 50 decibels to prevent the telemetry data signal from saturating the GPS antenna.